KR100789004B1 - A method of forming a channel on the surface of a metal substrate, and related articles - Google Patents

Abstract

A method of forming a channel (80) in a coated (72, 74) metallic substrate 54 is disclosed. One technique is to first deposit channel-forming material 50 onto substrate 54 and then to deposit a binder 58 such as soldering. One or more coatings 72, 74 may then be applied onto the substrate 54. In one embodiment, the channel 80 is formed when the channel-forming material 50 is subsequently removed. In another embodiment, the channel 20 is formed due to the lack of binding force between the particular channel-forming material 10 and the upper binder 18. Gas turbine components are also disclosed that include related products, such as protective coatings and patterns of cooling channels.

Description

A METHOD OF FORMING A CHANNEL ON THE SURFACE OF A METAL SUBSTRATE, AND RELATED ARTICLES             

1 shows a cross-section of a substrate in a processing step to form a channel, depicting the deposition of the channel-forming material.

2 shows a cross-sectional view of the substrate after depositing the binder and coating system on the channel.

3 is a micrograph of a cross section of a coating system in which a channel is introduced under a binder and attached to a metal substrate by a binder.

4-8 are detailed cross-sectional views illustrating steps of an exemplary and optional method for forming a channel in an article having one or more coatings.

The present invention generally relates to a method of forming hollow structures in the surface region of a coated metal substrate. In some specific embodiments, the present invention relates to a method of forming cooling channels at or near a surface of a hot product covered with a protective coating.

Various types of metals are used for components that may be exposed to high temperature environments such as airplane engine parts. Various approaches have been taken to raise the operating temperature at which metal components can be used. For example, one approach is to use a protective coating on various surfaces of components, such as gas turbine engine airfoils. The coating is typically ceramic based and is often referred to as Thermal Barrier Coating or "TBC".

TBCs are generally used with internal cooling channels in airfoils, through which cooling air is forced into the engine during engine operation. By way of example, the pattern of cooling holes may extend from the relatively cold surface of the airfoil to a “hot” surface exposed to gas flow at a combustion temperature of about 1000 ° C. or more. This technique is often referred to as "discontinuous hole film cooling."

In some cases, the cooling structure should be relatively close to the "hot" surface even when such surface is covered by a protective coating. For example, coolant, such as air, is often directed onto the outer surface of the turbine combustor liner (ie, "backside" cooling) and also passes through the inner surface of the turbine combustor liner. Cooling mechanisms of this type are generally disclosed in US Pat. No. 5,822,853 (Ritter et al.). Combustor liners typically have a thickness of about 1/10 inch (2.5 mm) to about 3/16 inch (4.7 mm).                         

Much work has been done to design appropriate patterns of cooling channels for sheet metal structures. For example, the litter patent describes the formation of cooling channels in cylindrical structures such as turbine combustors. In the technique of the litter, a double wall assembly is constructed. The assembly comprises an inner wall, channel-forming means, sacrificial channel filler and an outer wall. The channel-forming means is between two walls and filled with channel fillers. The assembly is hot-pressurized to join each wall to the other wall. Subsequent removal of the filler creates the desired cooling channel.

U.S. Pat.No. 5,075,966 to Mantkowski discloses a method of making cooling channels and other hollow structures. The surface of the substrate is optionally patterned and filled with a slurry. Once the solvent is removed, the slurry turns into a solid filler. A close-out layer is then deposited on the patterned surface and the filler. Subsequent removal of the filler forms the desired hollow structure. The Mankovsky method can be used to form hollow cooling channels in turbine engine components such as blades and vanes.

There are several advantages associated with the technology implemented in the Mankowski and Litter patents. However, the method can present several disadvantages for some uses. For example, the method must form grooves or channels in the metal surface. These features should generally be patterned and formed by some kind of casting or mechanical method. Casting and mechanical methods can be time-consuming. In addition, this technique is not always suitable for small-diameter structures, or structures of complex shape. The limitations of this method become more apparent when used for advanced applications, for example in channels in thin film superalloy structures.

Thus, novel methods for the formation of hollow structures in coated metal substrates are of great importance in the art. The method should avoid the use of casting or mechanical methods. The method should also be able to form a pattern of the structure, for example a complex pattern of cooling channels. The method should also be compatible with the method used to apply the coating to the substrate. It would also be advantageous if the novel method could easily change the shape of the hollow structure or the composition of the material forming the hollow area itself. This flexibility would be very advantageous for improving heat transfer properties in the case of cooling channels for gas turbine devices.

Disclosed herein are methods of forming one or more channels in a coated metal based substrate. The method includes the following steps:

(a) depositing a channel-forming material on a surface of the substrate in a pattern representing a selected channel shape;

(b) fusing the desired coating material with the lower binder to the surface such that the coating covers the channel-forming material and selected areas of the surface; And

(c) removing the channel-forming material to form the channel.

The channel-forming material can vary widely. In some embodiments, it is a sacrificial material that is subsequently removed to form a channel. General sacrificial materials are described below. In another embodiment, the channel-forming material is typically a "stop-off" composition. The stop-off substantially impedes adhesion between the binder and the substrate. Lack of such adhesion or "wetting" also results in the formation of channels. Thus, another embodiment for forming a channel includes:

(A) depositing a stop-off material on the surface of the substrate in a pattern representing a selected channel shape, wherein the stop-off material prevents adhesion between the substrate and a binder applied on the substrate and the stop-off material. Can be prevented);

(B) fusing the desired coating material to the substrate with a binder such that the coating covers the stop-off material and the selected area of the substrate, and the binder under the coating is substantially free of adhesion to the stop-off material, thereby closing the channel. Forming step.

The invention is particularly useful for the production of patterns of channels and the channel-forming materials are usually deposited in such a pattern. The channel pattern serves, for example, as a circuit for coolant flow in the wall of the turbine component. Different techniques for applying the channel-forming material to a substrate are described below, for example, directly or as prefabricated foils.                     

The binder is often a brazing material, for example nickel based brazing. Various techniques for applying the binder are described below. Briefly, this is generally a substrate; tape; The use of a slurry applied directly to the foil or pre-formed binder-channel-forming material structure.

As used herein, the coating materials vary widely. Typically, these are protective coatings designed to provide a substrate that is resistant to thermal or environmental degradation, as described below. In some embodiments, the coating material is a combined coat-TBC system frequently used on gas-turbine engine elements. The term "coating material" is often used herein simply in the singular form. The term should be understood to include both single and multiple coatings.

In addition, the coating material may be applied onto the substrate in a variety of ways, such as in the case of channel-forming agents. For example, the coating can be applied directly onto the substrate by plasma spraying. Alternatively, they can be pre-formed on a separate temporary substrate and bonded to the substrate.

Another embodiment of the invention

(I) a metal based substrate having a surface comprising one or more channels; And

(II) at least one coating disposed on the surface and the channel,

The coating relates to an article attached to a substrate with a binder. As described in more detail below, the substrate is often a superalloy product covered with one or more protective coatings. Such products also typically include a pattern of channels that can provide a variety of functions, such as acting as cooling conduits.

Further details of the various features of the invention are set forth in the remainder of the specification and in the accompanying drawings.

The metal substrate of the present invention can be made from various metals. The term "metal-based" is used herein to describe substrates which are formed predominantly of metals or alloys, but may also contain several non-metallic components. "Non-metal" refers to a material such as ceramics, or an intermediate phase. Typically, the substrate is a heat resistant alloy, for example superalloy having an operating temperature of generally about 1000 to 1150 ° C. The term "superalloy" is intended to include composite cobalt-, nickel- or iron-based alloys which typically include one or more other elements such as aluminum, tungsten, molybdenum and titanium. Superalloys are disclosed in many literatures. Nickel-based superalloys generally comprise at least about 40 weight percent Ni. Cobalt-based superalloys generally comprise at least about 30% Co by weight. The actual configuration of the substrate can vary widely. For example, the substrate may be in the form of various turbine engine components such as combustor liners, combustor domes, shrouds, buckets, blades, nozzles or vanes.

As used herein, the term "channel" refers to any hollow conduit through which liquid or gas can flow. For example, the channel may be in the form of a tubular sealed passage. Very often, the channels are cooling passages (“cooling channels”) for gas turbine components, as disclosed in US Pat. Nos. 5,075,966 (Mantkowski) and 5,822,853 (Ritter). All of these patents are incorporated herein by reference. Cooling channels formed by the present invention are typically located on the substrate surface. More often they are covered by one or more coating layers having a total thickness of about 1 mil (0.025 mm) to about 100 mil (2.54 mm).

In one embodiment of the invention, the channel-forming material (or “channel former”) is a stop-off material 10, as shown in FIG. 1. The stop-off material is deposited on the surface 12 of the substrate 14. The position relative to the open area 16 of the stop-off material generally determines the position of the channel to be finally formed. (For easier viewing, stop-offs are generally shown in FIGS. 1 and 2 longer than generally fit for this embodiment (though the dimensions may vary). As mentioned below, in some cases the stop- The off may only constitute a thin layer of oxide to be formed (eg thermally) on the substrate).

In this embodiment, the stop-off material 10 is one that can hinder the adhesion between the substrate and the binder subsequently applied on the stop-off material. One skilled in the art can determine the most appropriate material for the selected substrate and binder (disclosed below). In addition to impeding adhesion, certain stop-off materials should be able to be removed without heavy effort if it is desired to remove them. In that case, the removal conditions (eg thermal conditions) should not adversely affect the substrate or binder.

If the binder is a braze material, the stop-off material typically comprises a composition selected from the group consisting of metal oxides, metal salts and halide salts. In some preferred embodiments, metal oxide materials are preferred. Non-limiting examples include magnesium oxide, aluminum oxide, zirconia and yttria. If the binder is a high temperature epoxy or solder as described below, the stop-off composition is typically a metal oxide or metal salt.

The stop-off material is deposited in a pattern representing a selected shape of one channel or a plurality of channels. The shape of the channel can be determined according to its purpose. In this embodiment, the adhesive free channel between the stop-off and the binder is relatively recessed. For example, the channels typically have an average depth of about 5 to about 100 μm and an average width of about 20 to about 400 μm. As shown in FIG. 3 (disclosed below), the shape of the channel in this embodiment is somewhat irregular.

In some embodiments, the stop-off material is applied directly to the substrate surface. Techniques for applying stop-off materials are known in the art. For example, stop-off wires, rods and tapes are commercially available. They can be sized, cut and fused to the substrate surface to match the desired pattern. Optionally, the stop-off material may be deposited in slurry form by various types of slurry deposition techniques. The slurry can be applied in a desired pattern, for example by pouring it through a suitably shaped mask.

Stop-off materials can be readily applied to the surface by a variety of different deposition techniques. Non-limiting examples include screen printing, ink-jet printing, transfer printing, extrusion and various lithographic techniques. All such techniques are known in the art. For example, screen printing (eg silk screen printing) is described in "Encyclopedia Americana", Intl. Ed., Volume 24 (1999) and "The World Book Encyclopedia" (World Book Millennium 2000), Vol. 15]. Ink jet printing is described, for example, in "Encyclopedia Britannica", Vol. 21 Macropedia (1989) (for deposition techniques such as ink jet printing, the stop-off material is in fact a printing "ink"). Various lithographic techniques are described in "Encyclopedia Americana", Intl. Ed., Vol. 17].

As a variation on the direct-deposition technique, the stop-off material may be pre-formed before being applied to the substrate surface. For example, stop-off material may be deposited once on a removable support sheet (eg, decal backing) by various deposition techniques. The material may be deposited in a preselected pattern, for example by printing techniques. Non-limiting examples include screen printing, laser printing and LEDs disclosed in the above-mentioned documents "Encyclopedia Britannica" and ["Encyclopedia Americana"). In the case of laser printing, the preferred pattern of channels was introduced into the computer program as input-data. The program adjusts the laser beam and optical components to selectively etch the pattern-image on the photoconductor drum. The image on the drum can then be electrostatically transferred, for example, to the support sheet surface. Those skilled in the art can readily modify conventional printing methods to meet the various requirements of a stop-off “ink”, such as material viscosity, volatility, temporary electrostatic surface deformation, and the like.

After deposition (and heating or curing as needed), the support sheet is removed and the desired free-standing stop-off pattern is left, which can be applied as a decal (hereafter in another aspect of the present invention). As will be described, various techniques may be used to easily separate the material from the support sheet). The free upright stop-off material can then be attached to an optional region of the substrate surface by any conventional method. This embodiment is particularly useful when a number of small channels are formed (sometimes in a tangled pattern). This embodiment is also very useful when the substrate itself is severely curved or somewhat irregular.

As shown in FIG. 2, a binder 18 is then applied onto the surface 12. In this embodiment, the binder fills the open space 16 (see FIG. 1). The binder acts as an attachment site for the subsequently applied coating. Various types of binders can be used, depending largely on the composition of the substrate and the coating. If the substrate is a section of high thermal components, the binder is typically soldered, for example when it is made of a superalloy material. However, non-superalloy components used for low temperature applications may not require solder-bonding. Instead, various other binders may be used, for example high temperature epoxy or soldering. Although the teachings herein relate primarily to brazing materials, those skilled in the art will optionally use other binders in a similar manner.

Various braze alloy compositions can be used in the present invention. Some of them are described in "Kirt-Othmer Encyclopedia of Chemical Technology", 3rd Edition, Vol. 21, page 342 et seq. If the substrate is a nickel-based superalloy, the braze alloy typically contains at least about 40% nickel by weight (the nickel-containing braze alloy or cobalt-containing braze alloy is typically used with cobalt-based superalloys). The braze alloy composition may also contain silicon and / or boron, which acts as a melting point depressant.

Examples of nickel-based braze alloy compositions include the following. The components are expressed in weight percent:

1) 4.5 Si, 14.5 Cr, 3.3 B, 4.5 Fe, remaining Ni;

2) 15 Cr, 3.5 B, remaining Ni;

3) 4.5 Si, 3 B, remaining Ni;

4) 4.2 Si, 7 Cr, 3 B, 3 Fe, remaining Ni;

5) 10 Si, 19 Cr, rest Ni;

6) 3.5 Si, 22 Co, 2.8 B, remaining Ni;

7) 3.5 Si, 1.8 B, remaining Ni;

8) 4.5 Si, 14 Cr, 3 B, 4.5 Fe, remaining Ni;

9) 17 Cr, 9 Si, 0.1 B, remaining Ni;

10) 2.6 Si, 2 Cr, 2 B, 1 Fe, remaining Ni;

11) 15 Cr, 8 Si, remaining Ni;

12) 10.1 Si, 19.0 Cr, remaining Ni;

13) 4.5 Fe, 4.5 Si, 14.0 Cr, 3.1 B, 0.75 C, remaining Ni;

14) 4.5 Fe, 4.5 Si, 14.0 Cr, 3.1 B, remaining Ni;

15) 4.5 Si, 3.1 B, remaining Ni;                     

16) 11.0 P, remaining Ni;

17) 10.1 P, 14.0 Cr, remaining Ni; And

18) 19 Cr, 7.3Si, 1.5B, rest Ni.

Some preferred nickel-based braze alloy compositions of the present invention include at least one of silicon, chromium, boron and iron, with the remainder being nickel. Silicon is often preferred over boron. Sometimes a mixture of silicon and boron is used.

Examples of cobalt-based braze alloy compositions include:

1. 8 Si, 19 Cr, 17 Ni, 4 W, 0.8 B, remaining Co; And

2. 17.0 Ni, 1.0 Fe, 8.0 Si, 19.0 Cr, 0.8 B, 0.4 C, remaining Co;

It should be noted that precious metal compositions containing other types of braze alloys, such as silver, gold, and / or platinum, together with other metals, such as copper, manganese, nickel, chromium, silicon and boron, may be used. Mixtures comprising at least one of the braze alloy elements are also possible. Many metal braze compositions are commercially available from Praxair Surface Technologies, Inc.

When the binder 18 is a braze material, it is often applied in slurry form on the substrate 14. The slurry typically contains a braze material, a metal powder, a binder and optionally a solvent. The metal powder is often in the form of discrete particles of a base metal in a substrate, for example nickel.

Various binder materials can be used as the braze slurry. Examples include aqueous organic materials or solvent-based binders such as polyethylene oxide and various acrylics. Various mixtures are disclosed for slurry mixing, for example in US Pat. No. 4,325,754, which is incorporated herein by reference. Slurry compositions are also commercially available. It is advantageous in various situations to use the braze slurry composition. For example, if the final substrate surface is irregular or contains pits or crevices, a solder slurry can be used to fill these areas.

Various techniques are useful for applying the braze slurry composition. For example, it can be sprayed, painted or tape-cast directly onto the substrate. To fill the open space 16, the slurry (binder) 18 typically covers at least a portion of the top surface 19 of the stop-off layer 10. However, the slurry does not fully adhere to the stop-off material even after fusion as described below. Thus, a relatively small open area 20 remains around each stop-off 10. The open area 20 can act as a channel through which air can flow, for example. Any excess slurry applied on top surface 19 or stop-off layer 10 can be easily removed, for example by rubbing.

In another embodiment, the binder may be applied as a green solder tape on the substrate. Such solder tapes are disclosed in US Patent Application No. 09 / 304,276 (W.Hasz), filed May 3, 1999. The tape is commercially available. Alternatively, they can be formed from a slurry as described above (eg, cast on a removable substrate, dried and detached therefrom).                     

As another alternative technique for applying a solder binder to a substrate, a free upright solder foil can be used. Methods for using such solder foils are known in the art. The braze foils are also commercially available from various sources as disclosed in US Pat. No. 6,355,356, which is incorporated herein by reference. The solder foil can be tack-welded to the underlying layer or adhesive can be used.

1 and 2 typically include a braze material as a binder. However, it should be understood that the open area 20 may optionally be formed when using other types of binders, such as epoxy or the braze material described above. As in the case of soldering, a stop-off composition should be selected in which no other binder is substantially bonded. It is expected that the metal oxide or metal salt should be a sufficient stop-off material for this optional binder.

If the binder is a slurry or a green tape containing volatile components, a heating step can generally be performed to "cure" the bonding material. This step serves to remove any volatiles (or vaporize if not removed) by a subsequent high heat treatment, for example a plasma deposition step. If the bonding material is a soldering composition, conventional soldering operations are used for this step. The soldering steps and conditions are described in more detail later, as they involve the subsequent attachment of one or more coatings to the soldering. This soldering step is typically performed at very low pressure (eg less than about 10 ⁻¹ torr) or under vacuum.

In another embodiment, both the stop-off material and the binder may be preformed before being applied to the substrate surface as a single foil structure. In this embodiment, the stop-off material may first be deposited on the removable support sheet as described above. The binder, for example a solder-slurry material, is applied on the stop-off to form two layers (thus the two layers are the lower sublayers of the channel-forming material, ie in this case the stop-off, and the upper sub of the binder). Layer). Suitably, the stop-off and the composition of the solvent-binder system for the binder can be adjusted to ensure sufficient contact between the two.

As noted above, the binder remains small open regions (regions 20 in FIG. 2) that do not sufficiently adhere to the stop-off material and can act as channels. The support sheet is removed, leaving a free upright two layer comprising an intervening open area. These two layers may then be applied or attached to selected areas of the substrate surface (the stop-off surface is placed in contact with the substrate, and the opposite surfaces of the two layers, ie the binder layer, are facing outwards for subsequent coating deposition). Exposed). This two-layer structure may be temporarily placed on the substrate prior to fusion by various techniques. As one example, the two layers may be exposed to a solvent that partially dissolves and plasticizes any binder in the binder material such that the structure adheres to the substrate surface (this technique is described in patent application 09 / 304,276 above). Is disclosed in the heading).

As a further variant, the stop-off material may be deposited on a sheet of binder, for example on the brazing foil described above (the stop-off may be deposited in a constant pattern or later patterned by conventional techniques. Can be). This stop-off / foil structure is then attached to the substrate in the desired area, where the stop-off is in direct contact with the substrate. The structure may be temporarily held in place by various techniques. For example, an adhesive may be used. Optionally, the upper foil can be tack welded onto the substrate. Fusion of the stop-off / foil structure (eg soldering) may be performed by conventional techniques described below.

In the entire embodiment described above, there is no need to remove the stop-off material. In other words, the channel formed from the lack of adhesion between the stop-off and the binder already exists. However, sometimes it is desirable to remove the stop-off material, for example to slightly enlarge the channel size. Removal of the stop-off material is described in more detail below with respect to other embodiments. In this case, removal of the stop-off material may be performed before or after the deposition of one or more subsequent coatings on the solder.

As mentioned above, one or more coating materials are applied on the substrate to cover all or almost all of the binder. In some embodiments, the coating material is applied directly onto the substrate, ie on the binder. The choice of coating material will of course depend on the end use requirements of the product. For example, coatings can be used primarily for thermal protection, for example thermal barrier coatings (TBCs). Optionally, the coating is one that provides environmental protection, ie protection of the substrate from the adverse effects of oxidation, corrosion and chemical attack. The thickness of the coating material will depend on the material cost as well as the requirements of the product.                     

Frequently, the coating applied on the binder is metallic. Many different types of metallic coatings can be used. For turbine products, the metal coating also includes a material of the general formula MCrAl (X), where M is selected from the group consisting of Ni, Co, Fe, and combinations thereof. In the above formula, "X" is an element selected from the group consisting of Y, Ta, Si, Hf, Ti, Zr, B, C and combinations thereof. Some of the preferred alloys of this type comprise about 17 to about 23% chromium; Aluminum about 4 to about 13%; And yttrium in a broad composition (% by weight) of about 0.1 to about 2%, wherein M constitutes the remainder.

Other types of metal coatings may also be used. Examples include aluminide type coatings such as nickel aluminide or platinum-nickel-aluminate. Abrasion resistant coatings (often called "wear coatings") can also be used. Examples include those formed of chromium carbide or cobalt-molybdenum-chromium-silicon.

MCrAl (X) coatings such as those described above may themselves provide some degree of corrosion protection and oxidation protection to the substrate. However, such coatings are often used as a bonding layer for subsequently applied ceramic coatings, for example thermal barrier coatings. 2 depicts the presence of the bond coat 22 and the upper ceramic coating 24. Often, the ceramic coating is a thermal barrier coating. It is generally (but not always) zirconia. As used herein, “zirconia-based” includes ceramic materials containing at least about 70% by weight of zirconia. In a preferred embodiment, the zirconia is chemically stabilized by blending with a material such as chemically yttrium oxide, calcium oxide, magnesium oxide, cerium oxide, scandium oxide or any mixture of these materials.

As used herein, the coating material can be applied by many different techniques. The choice of specific technique will of course depend on the type of coating material to be deposited. For example, a metal coating (eg MCrAl (X) coating) can be applied directly to the substrate by thermal spraying techniques. Examples include air plasma spray (APS), vacuum plasma spray (VPS) and high speed oxygen-fuel (HVOF). Other deposition techniques can also be used, for example sputtering. Ceramic coatings (eg TBC) are generally APS; Applied by physical vapor deposition (PVD) or electron beam physical vapor deposition (EB-PVD).

As mentioned above, there is an alternative aspect of depositing the coating directly on a substrate. For example, the coating material (eg, a bond coat) can be preformed and applied onto the substrate, ie on a binder disposed on the substrate. To illustrate, the coating may be applied as a foil on the substrate, ie on a thin sheet, sometimes referred to as a "coating pre-form." Such techniques are disclosed in US patent application Ser. No. 09 / 411,222, which is incorporated herein by reference. The coating foil can be produced by various techniques. For example, the coating material may be deposited as a thin layer of metal, typically in powder form, onto a removable support sheet (usually metal). The powder may be applied to the support sheet by the thermal spraying technique described above or by sputtering, PVD, or the like.

After the coating is deposited on the support sheet, the latter is removed, leaving the desired free upright metal foil. Various techniques can be used to remove the foil from the support sheet. For example, if the support sheet is not intentionally grit-blasted prior to the deposition of the coating metal, the adhesion of the metal to the support sheet is relatively low and facilitates the detachment of the foil. Optionally, a conventional release coating may be applied to the removable support sheet prior to application of the coating material.

In addition, a plurality of coatings may be applied successively onto the bond coating on the removable support sheet. By way of example, zirconia-based TBCs can be applied onto the bond coat by a variety of techniques, such as APS. After detachment from the support sheet, the free upright foil includes both the bond coat and the TBC.

The foil may then be cut to a suitable size in place on the substrate for which the coating is intended before being fused to the substrate. Various techniques can be used to temporarily hold the foil in place prior to fusing. For example, an adhesive, ie, one that volatilizes completely during the fusing step, may be used. Optionally, the foil is tightened with screws, clamps or tacks in place.

The fusing step for attaching the foil of coating material to the substrate can be performed by various techniques. As mentioned above, it is usually performed as a conventional soldering operation. (As used herein, "soldering" is generally intended to include any method of joining metals, including the use of filler materials or alloys). One exemplary reference regarding soldering is as follows: "Modern Metalworking", J.R.Walker, The Goodheart-Willcox Co., Inc., 1965, pp. 29-1 to 30-24.

Those skilled in the art will know in detail about soldering. The brazing temperature depends in part on the type of braze alloy used and is typically about 525 to about 1650 ° C. For nickel-based braze alloys, the brazing temperature is typically about 800 to about 1260 ° C. If possible, soldering is often performed in a vacuum furnace. The degree of vacuum will depend in part on the composition of the braze alloy. Typically the vacuum is about 10 ⁻¹ torr to about 10 ⁻⁸ torr.

As mentioned above, the fusing step may be performed by techniques other than soldering. For example, a torch or other heating technique, such as a welding technique, can be used to fuse the coating foil to the substrate. This technique represents an alternative aspect to vacuum furnaces.

Regardless of which fusion technique is used, the resulting coating is metallurgically bonded to the substrate. Attachment of the coating to the substrate occurs through the binder layer. However, in this embodiment, there is no adhesion between the binder and the stop-off (as previously disclosed), so that no coating is substantially attached to the substrate in the region where the binder lies on the stop-off material. Thus, the channel (ie, open area 20 in FIG. 2) remains in the surface area of the coated substrate. In this embodiment, the channel is described as substantially a circumferential stop-off 10 (stop-off actually functions as the bottom surface of the channel). However, in any particular case the specific shape of the channel depends in part on the degree of "non-adhesion" between the stop-off 10 and the binder 18. In some cases, the channel may be slightly enlarged at this stage by removing the stop-off material.

3 is a micrograph of a cross section of a coating system applied onto a substrate. The substrate 30 is made of nickel-based superalloy. In the general region 32, represented by the reference number 32, a very thin oxide layer (not shown on the microscope) formed naturally on the surface of the substrate.

The coating system is a free upright preformed bondcoat / TBC foil. The preparation of such foils is disclosed in the aforementioned pending patent application Ser. No. 09 / 411,222. The foil comprises a NiCrAlY-type bond coat and upper zirconia-yttria TBC (both coatings were air plasma-sprayed onto the temporary substrate and then detached therefrom).

The coating foil was attached to the substrate with green solder tape. The tape had the following composition: 10 wt% Si, 19 wt% Cr, balance Ni. Vacuum-soldering was performed at 2100 ° F. (1149 ° C.) for 30 minutes. A solder layer having a thickness of about 0.001 inch / 0.025 mm can be seen in the general area 34 in FIG. 3 (for example, it should be understood that a solder foil as described above may be used in place of the solder tape).

In this exemplary embodiment, the bond coat 36 comprises two general areas. Region 38 is characterized by a general "sponge" microstructure derived from air-plasma injection of NiCrAlY material. Region 40 initially has the same microstructure but is subsequently infiltrated with the brazing material during heat treatment to densify the region. Coating 42 is a zirconia-based TBC.

3 shows that the foil-coating (ie, the bond coat 36 and the TBC 42) is completely soldered to the metal substrate 30 except in the region where the oxide layer is present, ie above the surface region 32. Oxide in this region acts as a stop-off and prevents wetting of the solder. Thus, voids or channels 44 were formed as described above. One or more other voids (or black areas) that act as channels are also shown around the same vertical position in the micrograph.

In another embodiment of the invention, sacrificial fillers are used as channel-forming agents. Removing the filler forms a channel. Thus, this embodiment does not depend on whether the binder is attached to the lower filler.

As shown in FIG. 4, the sacrificial filler 50 is once deposited on the surface 52 of the substrate 54, the position of the sacrificial filler relative to the open area 56 ultimately determines the geometry of the channel to be formed. do. As a non-limiting example, a combustion chamber for a gas turbine will need a cooling channel having an average width and height (depth) of about 0.005 inches (0.127 mm) to about 0.050 inches (1.27 mm). In a preferred embodiment, the cooling channel has an average width and height of about 0.010 inches (0.254 mm) to about 0.025 inches (0.635 mm). Thus, the sacrificial fillers have substantially complementary dimensions.

Various materials can be used as sacrificial fillers for this embodiment. Non-limiting examples include the stop-off materials described above (higher amounts of material are typically used in this embodiment). Various other inorganic compounds can be used as disclosed in US Pat. No. 6,321,449 to Zhao et al., Which is incorporated herein by reference. These include various metal oxides, metal halides, metal borates, metal sulfates, metal aluminates and combinations thereof. Some specific examples are sodium chloride, potassium borate, nickel chloride, magnesium sulfate, nickel fluoride, sodium aluminate and a mixture of sodium aluminate and sodium aluminosilicate. When used in paste form, many such inorganic compounds are combined with binders and / or solvents. Non-limiting examples of such binders are water based gels such as Vitta Gel®. The choice of particular solvent depends on the type of binder used. Specific examples include water, alcohols, acetone, sodium hydroxide solution and potassium hydroxide solution. Carbon-based materials such as graphite may be used as the sacrificial fillers.

As described above in this embodiment (ie, only the materials of the stop-off type are used), the sacrificial filler is deposited in a pattern representing the selected shape of the channel (s). In this embodiment, the filler of the desired volume is nonetheless sufficient to function as a "core" to the desired dimension of the cooling channel. The technique used for the deposition can also be used here as long as it is required to treat the required amount of filler, for example lithography or slurry deposition. In addition, the stop-off material may be previously formed on a separate support sheet and subsequently deposited on the substrate of the article as described above.

Some sacrificial materials, such as graphite, can react with certain binders, such as metal soldering. Thus, in some cases, it may be desirable to pre-coat the sacrificial material (eg graphite stick or tape) with one of the stop-off materials described above. This stop-off coating will function substantially to prevent a reaction between the sacrificial material and the binder. The sacrificial material will then be substantially removed during one of the fusion (heating) steps discussed below.

As shown in FIG. 5, a binder 58 is then applied onto the surface 52. The binder fills open space 56 (see also FIG. 4) and functions as an attachment site for the subsequently applied coating. (The binder will constitute the wall of the channel that will eventually be formed, as is evident in the subsequent figures). Suitable types of binders are described above. Soldering compositions are commonly used. The binder typically covers at least a portion of the top surface 59 of the sacrificial filler-layer 50 (FIG. 5). The binder may or may not be attached to the sacrificial material. Adhesion or lack thereof depends on various factors, such as material composition and density, but is not an important characteristic in this embodiment. If the binder is present as a semisolid, for example a slurry, excess can be removed after deposition. In addition, a heating step may be necessary to remove any volatile components from the binding composition (as previously described).

As in the embodiments discussed above, the sacrificial material and binder may be preformed as a single structure. This bilayer structure will be formed on the removable support sheet and detached from the support sheet. The structure can then be applied to the desired area of the final substrate. In another embodiment (and similar to the first embodiment), the sacrificial material may be applied directly to the binder's foil, such as a soldering foil. The foil will then be fused to the substrate.

In this step, one or more coatings may be applied onto the substrate as described above. As shown in FIG. 5, a binder 58 that can fill the open space 56 (see FIG. 4) and can also cover the sacrificial layer top surface 59 is typically sufficient to fuse the coating to the substrate. . However, in some preferred embodiments, especially when the binder is a braze material, a tape (sometimes called a "bond sheet") is applied prior to coating deposition. As shown in FIG. 6, the tape 70 is disposed on the binder 58 and the sacrificial layer 50. The tape provides a more uniform attachment site for the coating when stronger bonding is required.

In the case of a solder binder, the tape 70 is typically a solder sheet. Various types of solder tapes are disclosed in US Patent Application Serial No. 09 / 304,276 to W. Hasz. As an example, a green solder tape can be used. Such tapes are commercially available (eg, Amdry® solder tape). Optionally, they can be formed by various techniques, such as tape-casting a slurry of metal powder and binder in a liquid medium (eg, water or an organic liquid). Metal powders are typically materials similar to substrates (eg nickel- or cobalt-based compositions). Soldering tapes typically have a thickness of about 25 to about 250 μm and preferably a thickness of about 50 to about 250 μm (this type of solder foil is often about 10 to about 150 μm thick, more preferably about 10 to 40 μm thick).

The coating material is applied onto the substrate and covers tape 70 (or directly covers binder 58 and sacrificial layer 50 if no tape is used). 7 is illustrative and shows a bond coat 72 and the ceramic coating 74. However, as mentioned above, many different types of coatings (monolayer or multilayer) can be used. The coating can also be preformed on a separate substrate and then applied to the final substrate.

In embodiments in which the coating is preformed, conventional techniques can be used to ensure the size and shape of the channel. Slots or other holes can be cut (eg, mechanized) into the bottom surface (bottom) of the coated pre-groove. For example, the slot is cut into the underside of the bond coat in the bond coat / TBC bilayer structure. The shape of the slot can vary depending on requirements such as coolant flow efficiency. When the bilayer structure is attached to the substrate and heated, the binder fuses the bottom of the bilayer to the substrate surface. Because of the "cut-out" area, gaps will remain and act as shaped channels.

The fusion step is then carried out as described above. In the case of soldering binders, conventional soldering operations are carried out. The soldering step densifies the binder and provides a firm adhesion between the coating and the underlying substrate. As already described, selective heating techniques are possible to perform the fusing step, for example torch-welding.

As shown in FIG. 8, the sacrificial filler 50 is removed to form the desired channel 80. Various techniques are useful for removing sacrificial fillers. Much is disclosed in US Pat. No. 5,075,966 and US Pat. No. 6,321,449 as described above. The choice of specific technique will depend in part on the composition of the filler. The technique used should be such that it does not adversely affect the substrate, the binder or the coating material (eg, strong acids can remove many types of sacrificial fillers but can also damage metal components).

Water washing can be used as a removal technique for water soluble sacrificial materials. Chemical bleaching or vacuum extraction can be used for other types of materials. Etching with solvents such as water, alcohols, acetone or alkali metal hydroxides may also be used. Sometimes another suitable technique is ultrasound removal.

If the sacrificial material is organic or partially organic, combustion can be used. For example, the component may be heated to a temperature high enough to volatilize or burn off the sacrificial filler. Residue debris can then be removed by air-blasting alone or in combination with one of the techniques described above. In embodiments in which the coating material is applied on a direct binder by high temperature techniques, such as plasma technology, the plasma temperature will be sufficient to volatilize the sacrificial material.

As another embodiment, the sacrificial filler may be removed at an early stage of the method. For example, the filler may be removed after deposition and curing of the binder 58 (FIG. 5). The filler may also be removed after the application of the optional bonding tape, for example the braze tape discussed above. However, if the subsequent coating deposition method is carried out at a high temperature, for example in a plasma method, the filler often remains in place until the coating deposition is completed. This prevents any deformation of the final channel during coating deposition.

Another embodiment of the invention relates to an article made according to the method described above. Thus, the article includes a metal substrate 54, as shown in FIG. 8, which is often (but not always) formed from a superalloy material. One or more channels 80 are introduced into the article, generally on top of the substrate surface 52 (in this embodiment, as shown in FIG. 6, the cooling channels initially contain sacrificial fillers, for example fillers ( Substantially 50). The side walls of the channels are generally formed by the binders described above. As suggested above, the shape of the channel can vary widely. By way of non-limiting example, they may be shaped and positioned as “grooves” or “depressed interior regions” as disclosed in US Pat. Nos. 6,321,449 and 5,075,966, respectively, as indicated above. The cooling channels introduced into the turbine engine element will generally be in a pre-selected pattern according to their specific action.

The article further includes one or more coatings disposed on the substrate and the channel. For example, FIG. 7 depicts the bond coat 72 and ceramic film 74 as described above. The general thickness of such coatings is mentioned above and is also disclosed in US patent application Ser. No. 09 / 411,222. The coating is fused to the substrate by the binder discussed above, for example an intervening layer of braze material.

Another embodiment relates to an article made when the use of a stop-off material, as described above, prevents substantial adhesion of the upper binder. Thus, the stop-off material generally forms the bottom surface of the channel. The purpose protective coatings indicated above may also be used for this type of product.

Having described the preferred embodiments of the present invention, it will be apparent to those skilled in the art that the alternative embodiments do not depart from the spirit of the present invention. Optionally, it is understood that the scope of the present invention is limited only by the appended claims.

Conventional channel formation methods require time-consuming methods such as casting or mechanical methods, but according to the method of the present invention, it is possible to form a complex pattern of channels without using these time-consuming steps, and to change the shape and composition of the channels. It can be changed easily.

Claims (10)

A method of forming one or more channels 80 in a coated metallic substrate 54, (a) depositing a channel-forming material (50) on a non-patterned portion of the surface (52) of the substrate (54) in a pattern representing a selected shape of the channel (80); (b) a desired coating material 72, 74 is applied to the surface 52 and fused by the lower binder 58 to fill the space defined by the binder 58 by the channel-forming material 50. Causing the coating material (72, 74) to cover the channel-forming material (50) and selected areas of the surface (52); And (c) removing the channel-forming material (50) to form the channel (80). The method of claim 1, And the channel-forming material (50) comprises a composition selected from the group consisting of metal oxides, metal halides, metal borates, metal sulfates, metal aluminates, carbon-based materials and combinations thereof. The method of claim 2, And the channel-forming material (50) further comprises at least one component selected from the group consisting of a binder and a solvent. The method of claim 2, Channel-forming material 50 consists of sodium chloride, potassium borate, magnesium sulfate, nickel chloride, nickel fluoride, sodium aluminate, sodium aluminosilicate, magnesium oxide, aluminum oxide, zirconia, yttria, graphite and combinations thereof A method comprising one or more components selected from the group. The method of claim 1, The binder (58) is a braze material. The method of claim 1, The desired coating material (72, 74) is in the form of a free-standing coating foil fused by a binder (58) to the substrate (54). The method of claim 1, The desired coating material (72) is a metal coating. A method for forming a cooling channel (80) in a superalloy substrate (54) covered by a metal bond coat (72) and an upper thermal barrier coating (74), (I) a free layer comprising a lower sublayer 50 of the channel forming material and an upper sublayer 58 of the brazing material in contact with a pre-selected area of the substrate surface 52 and having a shape representing the selected shape of the cooling channel. Attaching the upstanding bilayer foil to the surface 52 of the substrate 54; (II) the bond coat 72 and heat shield coating 74 are fused to the substrate surface 52 by a braze material 58 such that the bond coat and the heat shield coating are formed of the channel-forming material 50 and the substrate. Covering a pre-selected area of the surface; And then (III) removing the channel-forming material (50) to form the target channel (80). delete delete

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